The present invention relates to a control system for a throttle valve actuating device for actuating a throttle valve of an internal combustion engine, and more particularly to a control system having a function for determining abnormality of the throttle valve actuating device.
In a throttle valve actuating device including a motor for actuating a throttle valve and configured so that the throttle valve is biased to be maintained at a fully-closed position when an electric current is not supplied to the motor, a method for detecting an abnormality such that the throttle valve does not normally operate is disclosed in Japanese Patent Publication No. 2538731.
According to this method shown in this publication, it is determined that there is an abnormality, when the throttle valve opening detected by a throttle opening sensor is not in the vicinity of a fully-closed opening in the condition where the electric current supply to the motor is stopped.
In the above conventional method, the abnormality determination is performed in the condition where the current supply to the motor is stopped. Accordingly, the opportunity for executing the abnormality determination is limited so that the detection of abnormality may sometimes be delayed.